Generally, angles of a headrest of sofa can be adjusted to improve comfort. One of the achievement manners is to set a headrest support in the sofa. The headrest support includes two fasteners, an electric push rod and a plurality of linkages, therein one fastener is fixed to the sofa body, another one is fixed to the headrest, the electric push rod is for driving the linkages to fold or unfold to change the relative position of the two fasteners, so that the angles of the headrest can be adjusted.
As shown in FIGS. 1 and 2, a conventional electric push rod 9 includes a drive motor 91, an outer tube 92, a threaded rod 93 and a slider block 94. Specifically, the outer tube 92 is hollow and fixed to the drive motor 91, the threaded rod 93 is located in the outer tube 92 and driven by the drive motor 91. The slider block 94 is sleeved on the outer tube 92 connected with the threaded rod 93 in the outer tube 92 via a screw hole 95, and then the slider block 94 is fixed to the linkages of the headrest. When the drive motor 91 is started up, the slider block 94 will move upwards or downwards to achieve the adjustment of the headrest angles.
However, such electric push rod has following disadvantages. Since the slider 94 is moved along with the rotation of the threaded rod 93, thus when the headrest is retracted to fold, the continuous movement of the slider block 94 may jam user's hands or fingers if the hands or fingers are rested under the headrest.
Thus it's necessary to provide an electric push rod that can prevent user's hands or fingers from being jammed, so as to ensure the user safety.